tamerlan is the one who carjacked the car. his little brother was nearby, we're told by a source in the investigation. so that's how it played out. but, boy, you are right, erin, what a crazy night. and it's taken this long. i think it's really taken this long for the police to figure it all out. >>> well, drew griffin, thanks very mump. we are learning now about where and how the brothers may have gotten some of the explosives that they used in the bombings. this has been another huge question mark out there. >> reporter: erin, cnn is told tonight that tamerlan, at one point, purchased a very large cachet of firearms. >> william says that this purchase took place on february 6th. he stressed at the time, it was not out of the ordinary. he says tamerlan asked the clerk what is the loudest and biggest thing that you have. he paid about $200 in this purchase. and, again, the purchase was two reloadble mortar kits with about 48 reloadble shells. >> thanks to you, brian. >>> one of tamerlan's closest friends, a man named brendan m